Power semiconductor components, such as IGBTs, are used for switching high currents and high voltages in variety of devices. Such devices include power converters that are used for converting electrical power from one form to another. Power converters comprise one or more power semiconductor components that are employed as switches.
When a power semiconductor component is used as a switch, the component operates between a fully conducting state and a blocking state. In the conducting state the switch component provides a low impedance current path and in the blocking state the switch component blocks the current and holds the voltage over the component.
A driver circuit is employed for controlling a power semiconductor component in a desired manner. For an IGBT component, a driver circuit produces a gate voltage to the gate of the IGBT. A positive voltage with reference to the emitter of the component is provided to turn the component on. The turn-off of an IGBT component is obtained when the gate is drawn to a negative potential with respect to the emitter. Thus for controlling the power semiconductor component, a driver circuit is used, which is able to produce suitable voltages to the emitter of the component.
In a simple form of gate driver, the gate driver produces a positive voltage to the gate when the gate driver receives a gate control signal to turn-on the component. Correspondingly, when a gate control signal to turn-off the component is received, the driver circuit produces a suitable lower voltage to the gate of the controlled component. The gate control signal may be a logic level signal having high and low states, and the states are interpreted as turn-on and turn-off commands of the controlled component.
For producing the required positive and negative voltages for controlling the power semiconductor component according to the gate control signal, the gate drivers receive a high auxiliary voltage and a low auxiliary voltage, which may be positive auxiliary voltage and a negative auxiliary voltage. These voltages are led to the gate of the controlled component using a pair of switches in the driver circuit. The pair of switches is typically connected in series across the positive and the negative auxiliary voltage, and upper switch is controlled conductive for turning-on the controlled component while the lower switch is controlled conductive for turning the component off.
It is further known that a gate resistance is connected in the output of a driver circuit. The gate resistance limits the current from the output switches of the driver circuit and thereby affects the speed of the state change of the controlled power semiconductor component. Different gate resistors may be employed for turn-on and for turn-off so as to change the properties of turn-on and turn-off independently from each other. The use of two gate resistors also enables to use a soft turn-off procedure, in which the resistors are connected in series using the output switches for a short period of time to produce a lowered gate voltage. The soft turn-off procedure is used in connection with over currents through the controlled component such that the high current is not shut-down too quickly.
One of the problems associated with the known gate drivers is that they are not able to drive the controlled power semiconductor component, such as an IGBT, in an efficient and controlled manner in which the different periods of turn-on and turn-off processes can be taken into account. Further, the known gate drivers do not enable to control the on-state gate voltage or to select different turn-on or turn-off speeds during the operation of the device, as these speeds are governed by the gate resistors.
Document EP 2178211 B1 shows a gate driver arrangement, in which gate voltage from the gate driver is in a form of a pulse width modulated (PWM) signal. In this arrangement, a PWM signal is amplified by output switches of the gate driver. The pulse ratio of the PWM signal is varied based on stored reference values on the basis of measured current. Although this arrangement increases the versatility of control of the switching periods, the arrangement is complicated and requires fast components. Further, in the arrangement, the average gate voltage level may be set using selected PWM patterns. However, to control the switching periods of a power semiconductor component efficiently, also the current produced by the gate driver is of importance. With the arrangement of EP 2178211 B1, the current to the gate of the controlled component cannot be set to a desired level in all desired periods of controlling the component.